Free radical- mediated damage to lipids and proteins, altered mitochondrial electron transport chain activities and abnormal patterns of tissue metabolism are strongly implicated in the pathophysiology of neurological morbidity caused by global cerebral ischemia and reperfusion. The overall objective of this project is to characterize the relationships between these factors and to relate them to the neurological impairment observed with animals subjected to a clinically relevant scenario consisting of cardiac arrest followed by 30 minutes to 24 hours of restoration of spontaneous circulation. The specific aims of these studies are to test the following hypotheses: (1) A short period of global ischemia causes immediate and reversible alterations in mitochondrial respiratory and Ca2+ uptake activities that are distinguishable from delayed, reperfusion-induced alterations. (2) Free radical damage due to cerebral ischemia/reperfusion adversely affects proteins as well as lipids present within mitochondria and other cellular compartments and membranes. (3) Mitochondrial membrane damage and enzyme inactivation result in immediate and delayed alterations in cerebral energy metabolism following cardiac arrest and ROSC. (4) Clinically-feasible manipulations of inspired and brain 02 concentrations alter the degree of molecular, subcellular, and metabolic injury, corresponding to differences in the extent of neurological injury observed following these different resuscitation protocols. Methods of approach to these aims will include measurements of 02 consumption, peroxide formation and Ca2+ uptake by isolated brain mitochondria and digitonin-permeabilized synaptoneurosomes and PC12 pheochromocytoma cells; determinations of lipid and protein oxidation, measurements of phospholipid and free fatty acid moieties and determinations of metabolic activities associated with glycolysis and the TCA cycle. Additional support for involvement of specific subcellular and metabolic alterations in the pathogenesis of ischemia/reperfusion brain injury will come from comparison of results obtained with different animal treatment protocols as well as with neurochemical measurements and histological testes. In vitro modeling of cellular and subcellular injury will also assist in the elucidation of cause and effect relationships. The significance of these studies is that they will provide unique molecular insight into the roles that altered bioenergetics and free-radical-metabolism play in brain injury associated with cardiac arrest and resuscitation as well as other forms of cerebral ischemia including stroke and trauma.